1. Field of the Invention
The present invention relates to a plasma tube array and a gas discharge tube used for the plasma tube array, in which plural light emitting tubes each having fluorescent material layers inside are lined up, and electric discharge is generated within those plural light emitting tubes so as to allow the fluorescent material layers within the light emitting tubes to emit light, thereby displaying an image.
2. Description of the Related Art
In general, as a large size image display apparatus performing an auto light generation, there has been disclosed a technique which makes use of a principle of plasma display to allow the light emitting thread made of tube (glass tube) of glass having fluorescent material layer and the like inside to line up in a large number and control light emission for each portion of each light emitting thread, thereby displaying an image (Japanese Patent Laid-Open No. 61-103187).
An individual light emitting thread is a thread, which forms an MgO layer and a fluorescent material layer, and for example, seals a discharge gas made of Ne and Xe into the glass tube. The fluorescent material layer is formed on a support member referred to as a boat, which is a mounting part having a cross sectional shape close to a semi-circle, and the support member (boat) is inserted into the glass tube. After that, the glass tube is evacuated, while being heated inside a vacuum chamber, and after being filled up with the discharge gas, both ends thereof are molten and sealed. The light emitting threads thus prepared are lined up and fixed in a large number, and at the same time, electrodes are provided above and below those light emitting threads, and those electrodes are applied with voltage, whereby discharge is generated inside the light emitting threads so as to allow fluorescent materials to emit light.
FIG. 1 is an oblique view showing a basic structure of the plasma tube array.
The plasma tube array (PTA) 100 shown here is disposed with light emitting threads 10R, 10G, 10B, 10R, 10G, 10B . . . incorporating therein fluorescent material layers that emit fluorescent lights of red (R), green (G), and blue (B), respectively. Each of the light emitting threads 10R, 10G, 10B, 10R, 10G, 10B . . . sealed with the discharge gas is sheet-like and lined up mutually in parallel. The front surfaces and rear surfaces of a large number of those lined up light emitting threads 10R, 10G, 10B, 10R, 10G, 10B . . . are disposed with a transparent front surface support substrate 20 and a transparent rear surface support substrate 30, respectively, and a large number of those lined up light emitting threads 10R, 10G, 10B, 10R, 10G, 10B . . . are formed so as to be held by the front surface support substrate 20 and the rear surface support substrate 30 between them.
Further, on the front surface support substrate 20, there are formed pairs of display electrodes 21 mutually extending in parallel, which are made of two pieces of display electrodes 211 and 212 in the lined up direction of a large number of light emitting threads 10R, 10G, 10B, 10R, 10G, 10B . . . , that is, in the direction to cross a number of those light emitting threads 10R, 10G, 10B, 10R, 10G, 10B . . . . This pair of display electrodes 21 is lined up in plural numbers in the longitudinal direction of the light emitting threads 10R, 10G, 10B, 10R, 10G, 10B . . . . Further, two pieces of display electrodes 211 and 212 making up one pair of display electrodes 21 have bus electrodes 211a and 212a made from metal (for example, Cr/Cu/Cr) formed at a mutually isolated side, respectively, and transparent electrodes 211b and 212b made up of an ITO thin film formed at a mutually adjacent side, respectively. The bus electrodes 211a and 212a are for lowering the electric resistance of the display electrodes 211 and 212, and the transparent electrodes 211b and 212b are devices for performing a bright display by allowing emission lights to transmit toward the front surface support member 20 side without shutting out the emission lights at the light emitting threads 10R, 10G, 10B, 10R, 10G, 10B . . . . Here, the pair of electrodes 21 may be formed of not only the transparent electrodes, but also the electrodes having a structure of high opening ratio such as mesh electrodes and the like.
Further, on the rear surface support substrate 30, there are formed multiple metallic signal electrodes 31. The signal electrodes 31 extend mutually in parallel along the respective multiple lined up light emitting threads 10R, 10G, 10B, 10R, 10G, 10B . . . , with the correspondence therebetween.
In case the PTA 100 thus formed is seen two-dimensionally, a cross over portion with the signal electrode 31 and the pairs of display electrodes 21 becomes a unit light emitting area (unit discharge area) The display is performed in such a manner that either one of the display electrode 211 or 212 is used as a scanning electrode, and at the cross over portion with the scanning electrode and the signal electrode 31, a selective discharge is generated so as to select a light emitting area, and accompanied with this discharge, by utilizing a wall charge formed in the inner surface of the light emitting thread in the light emitting area, the display discharge is generated between the display electrodes 211 and 212. The selective discharge is an opposed discharge, which is generated inside the light emitting thread between the scanning electrode and signal electrode 31 that are opposed above and below, and the display discharge is a surface discharge, which is generated inside the light emitting thread between the display electrodes 211 and 212 disposed in parallel on a flat surface. Through such electrode arrangement, the interior of the light emitting thread is formed with plural light emitting areas in the longitudinal direction.
Here, though the electrode structure of the drawing is a structure in which three electrodes are disposed in one light emitting area, and it is a structure in which the display electrodes 211 and 212 generate the display discharge, but it is not intended to be limited to this, and it may be a structure in which the display discharge is generated between the display electrodes 211 and 212 and the signal electrode 31. That is, it may be an electrode structure of the type in which the display electrodes 211 and 212 are made one piece, and this one piece of the display electrode is used as a scanning electrode so as to generate the selective discharge and the display discharge (opposed discharge) with the signal electrode 13.
FIG. 2 is a schematic illustration showing a structure for one pixel of the plasma tube array 100 shown in FIG. 1.
Here, three pieces of light emitting threads 10R, 10G, and 10B are shown. Each of the light emitting threads 10R, 10G, and 10B has a protective film 12 of a material such as MgO or the like formed in the inner surface of the glass tube 11, and is formed such that, inside the glass tube 11, there is inserted a boat 13 which is a support member formed with each of the fluorescent material layers 14R, 14G, and 14B that emit each fluorescent light of each color of R, G, and B (see Japanese Patent Laid-Open No. 2003-86141).
FIG. 3 is a view showing a boat in which the fluorescent material layer is formed.
The boat 13 is shaped in a semi-circular in cross section or shaped similarly to it, and has the same long extended shape as the glass tube 11 (see FIG. 2), and in the interior thereof, there are formed three types of the fluorescent material layers 14R, 14G, and 14B (see FIG. 2; in FIG. 3, they are collectively referred to as a fluorescent layer 14) corresponding to three types of the light emitting threads 10R, 10G, and 10B as shown in FIGS. 1 and 2.
Referring back to FIG. 2, the description will be continued.
Each of the light emitting threads 10R, 10G, and 10B shown in FIG. 2 is made up with the boat 13 of the shape shown in FIG. 3 inserted inside the glass tube 11. In FIG. 2 is shown that, on these light emitting threads 10R, 10G, 10B, there are disposed a pair of display electrodes 21 having two pieces of display electrodes 211 and 212. These two pieces of display electrodes 211 and 212, as described above, are made up of the metallic bus electrodes 211a and 212a and the transparent electrodes 211b and 212b. 
Here, in the case of the structure shown in FIG. 2, three pieces of light emitting threads 10R, 10G, and 10B having three types of the fluorescent material layers 14R, 14G, and 14B, respectively are made one set, and moreover, an area D1 defined by a set of the pair of display electrodes 21 having two pieces of display electrodes 211 and 212 becomes one pixel (1 pixel), which is a unit of a color image display. The diameter of each of the light emitting threads 10R, 10G, and 10B is typically approx. 1 mm, and in the case of the structure shown in FIG. 2, the size of the area D1 of one pixel is 3 mm×3 mm.
Here, the glass tube 11 used in the light emitting threads 10R, 10G, and 10B is difficult to make significantly smaller in diameter than a diameter of 1 mm due to necessity of securing the strength. Further, even if the glass tube of a small diameter can be prepared, the smaller in diameter the glass tube is made, the more it is difficult to dispose a protective layer and a fluorescent material layer inside the glass tube. Hence, to realize the light emitting thread made significantly smaller in diameter than a diameter of 1 mm, a significant increase of the cost is anticipated.
In the meantime, it is desired to display a highly precise image, which does not have a size of one pixel larger than 3 mm×3 mm, but smaller than that size.
In Japanese Patent Laid-Open No. 2003-272562, there has been disclosed a structure, which disposes a boat having two walls extending in the longitudinal direction inside the flat glass tube, and mounts three types of the fluorescent material layers emitting fluorescent lights of three colors of R, G, and B inside the boat. The technique of this patent publication adopts a flat glass tube aiming at reducing the number of glass tubes, and lines up and disposes three types of the fluorescent material layers extending in the longitudinal direction of the glass tube within one piece of that glass tube. When such arrangement can be realized within the glass tube having a diameter of approx. 1 mm, three types of the fluorescent material layers are lined up in the diameter direction of one piece of the glass tube, and the size of the pixel can be reduced by ⅓ (1 mm) with respect to the diameter direction of the glass tube.
However, according to the technique of this patent publication, since two pieces of rib-shaped partitions extending in the longitudinal direction for compartmentalizing three types of the fluorescent material layers in the boat are formed, there is a problem that the opening portions for emitting the fluorescent lights are narrowed by those partitions, thereby displaying a dark image. Further, assuming that the boat in the shape of having removed these partitions is prepared, and three types of the fluorescent material layers are coated according to the patent document, the shapes of the fluorescent material layers at both sides and the fluorescent material layer in the center become dissimilar, and from among three types of the fluorescent material layers, one type of the fluorescent material layer in the center alone differs from the others in the light emission efficiency due to difference in its shape.